Abstract
BACKGROUND: Adverse pregnancy outcomes (APOs) affect ∼20% of pregnancies and pose significant health risks for mothers and fetuses. Identifying risk factors is crucial for developing prevention strategies. OBJECTIVES: This study examined the association between vitamin D status, measured by 25-hydroxyvitamin D (25(OH)D) concentrations, and APO risk, and whether this association varies by pregnancy timing and body mass index (BMI) (kg/m(2)). METHODS: In this ancillary analysis of the Vitamin D Antenatal Asthma Reduction Trial, we used multivariable logistic regression models to examine the association between 25(OH)D concentrations in early (10-18 wk) and late (32-38 wk) pregnancy, and development of a composite APO outcome, including pre-eclampsia, gestational hypertension, gestational diabetes, intrauterine growth restriction, and preterm birth. RESULTS: Among 816 participants in the intention-to-treat analysis, 283 composite APO events occurred. Vitamin D supplementation did not significantly reduce APO risk. Participants who developed APOs had lower baseline 25(OH)D concentrations than those who did not (mean ± SD: 21.72 ± 10.04 vs. 23.47 ± 10.29 ng/mL; mean difference ± SE: 1.75 ± 0.78; P = 0.026). A significant interaction was observed between baseline 25(OH)D and BMI (interaction term, odds ratio [OR]: 1.04; 95% confidence interval [95% CI]: 1.00, 1.08; P = 0.041). Among participants with BMI < 25 (reference group), each unit increase in baseline 25(OH)D (ng/mL) was associated with 4% lower odds of developing an APO (OR: 0.96; 95% CI: 0.93, 0.99; P = 0.013), whereas no association was observed among participants with BMI ≥ 25 kg/m(2) (OR: 1.00; 95% CI: 0.98, 1.02; P = 0.83). Third-trimester 25(OH)D concentrations did not differ between participants with and without APOs. CONCLUSIONS: Although vitamin D supplementation did not reduce APO risk, higher early pregnancy 25(OH)D concentrations were associated with lower odds of APOs in participants with BMI < 25. These findings highlight the potential importance of higher early pregnancy 25(OH)D concentrations, particularly among those with normal BMI, in reducing APO risk. TRIAL REGISTRATION: This study is an ancillary analysis from VDAART, which is registered with ClinicalTrials.gov (NCT00920621: https://clinicaltrials.gov/study/NCT00920621?term=vdaart&rank=1).